-LRB- CNN -RRB- -- I 've written quite a bit about medical myths , so I 'm always a bit skeptical about medical `` knowledge . '' But one thing I , and I 'm sure many of you , think we understand is obesity . After all , weight issues crop up in media constantly . Just last night , Gov. Chris Christie was joking about donuts and his weight on The Late Show with David Letterman , and the First Lady 's weight is once again a subject of discussion in the Washington Post -- even though by any objective standard she 's in great shape .

We know how people gain weight , and we think we know how to lose it .

Except a study in this week 's New England Journal of Medicine shows us that 's just not right . Pretty much everything we `` know '' about obesity and weight loss is wrong .

Let 's start with some things that are true .

More than a third of Americans are obese . Many more are overweight . The Centers for Disease Control and Prevention estimates that obesity-related medical costs were almost $ 150 billion in 2008 , and the cost in health related expensed for an average person who was obese was more than $ 1,400 . This does n't count the physical , mental or quality-of-life toll that obesity can levy on a person .

Few of us dispute that we need to do something about this problem . There are plenty of experts -LRB- present company included -RRB- who will tell you what needs to be done . The sad truth , though , is that lots of that advice -LRB- even mine -RRB- turns out to be mistaken .

I know I 've told people that making small , sustained lifestyle changes is the best way to lose weight over time . But it turns out that making such changes , say by deciding to walk a mile every day for five years , results in far less weight loss than you 'd expect .

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I 've lectured people about the importance of physical education in schools , and I 've seen countless reports declaring that the decrease in PE nationwide is one of the reasons that more children are obese or overweight today . It turns out that studies do n't show that 's the case .

My family loves watching `` The Biggest Loser . '' But I 've found myself telling my kids again and again that what 's shown on TV is n't the best way to lose weight . I tell them that slow and steady works better in the long-run than rapid weight loss . I also tell them that setting unrealistic weight goals can actually sabotage your efforts .

So imagine my shock to discover that what evidence exists in this new study hints towards ambitious goals being a good thing , and that quicker weight loss is n't less likely to be kept off in the long-term .

People will say eating breakfast is a good idea when you 're trying to lose weight , because it will keep you from binging later . But studies show that there 's no protective effect from eating breakfast at all . People will say that eating more fruits and vegetables is a great way to lose weight . But studies show that , on their own , eating more of them without making other behavioral changes does n't result in any weight loss . There 's no magic to fruits and vegetables .

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People will say that snacking in between meals can lead to weight gain . But studies do n't show that to be the case either . In general , people compensate for snacking throughout the rest of the day . In other words , it 's not necessarily bad to snack outside of usual meal times .

It 's all enough to cause one to despair . But just because so much of what we believe is wrong does n't mean we still ca n't do something about the issue .

Studies do show that you can absolutely overcome genetic and familial factors to lose weight .

They show that significant physical activity can help with weight loss , and that it has the added bonus of making you healthier in general . Reducing your caloric intake works overall , especially if it 's done in a way to change your overall eating habits . Getting the whole family involved is important . And finally , for some , bariatric surgery can result in life-changing outcomes .

Over the past five years , my wife and I have lost quite a bit of weight . I 'm down somewhere between 15 % to 20 % of my high of more than 200 pounds . My wife lost even more , although I 'm not going to give you any numbers -LRB- I like being married -RRB- .

Now that I look back , if I 'm going to be honest about it , I did it in bursts over a few months here and there , each time gaining back less than I had lost .

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Each time , I had ambitious goals of 15 pounds or more in two to three months , and each time I really restricted my caloric intake . But I 've kept the weight off by radically changing my overall eating habits .

My breakfast consists of just coffee , I eat very light lunches , such as salads , and dinner is usually a healthy home-cooked meal with the family . My wife cooks way more than she used to and is obsessed with finding ways to make meals healthier . I avoid fried foods almost entirely , and I ca n't remember the last time I ate in a fast food restaurant . I also get to the gym two to three times each week .

I do n't tell you this because I think this is what you should do , or because I think it 's the key to getting thinner . I tell you this because more and more , I think that the journey to sustained weight loss is a very personal and individual path . Perhaps our problem is we 're trying to find a one-size-fits-all solution . I 'm not sure that exists .

Lastly , what was left out of this new scientific paper was prevention . The single best way to fight obesity is to avoid it in the first place . That has to start when kids are young , and it 's a lifelong journey . But one thing I doubt will ever be proved false is that it 's much easier not to gain the weight in the first place than to take it off later .

The opinions expressed in this commentary are solely those of Aaron Carroll .

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Aaron Carroll : I thought I knew all about obesity ; a new study challenges that

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He says obesity a big problem , but weight loss not as simple as fruits , veggies and no snacks

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Studies do show that overall , vigorous exercise and watching calories help

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Carroll : Best tool against obesity is not to get there in first place